Automatic limit bridge



Feb. 2, 1954 J. c. BREGAR AUTOMATIC LIMIT BRIDGE Filed Sept. 1, 194a.

efasga dirqya ATTORN EY Patented Feb. 2, 1954 AUTOMATIC LIMIT BRIDGE Joseph C. Bregar, Winston-Salem, N. 0., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application September 1, 1948, Serial No. 47,202

'7 Claims.

This invention relates to automatic limit bridges and more particularly to a limit bridge circuit comprising two conventional Wheatstone bridges electrically separated by two rectifier units, which is used for tolerance testing circuit elements.

In the past, attempts have been made to uti lize two separate Wheatstone bridges wherein an element to be tested was connected in common with the two bridges. One of the bridges contained a standard low limit resistance arm, the other bridge contained a standard high limit resistance arm. The two bridges were then balanced so that current responsive indicating means connected across each of the bridge circuits would indicate an unbalance in either of the bridges in the event that the element to be tested did not fall within the required tolerance range. This method of testing necessarily involved rather tedious adjustment of each of the bridges inasmuch as the current flowing through the common arm containing the element to be tested was a combination of the currents from each of the two bridges. A further disadvantage encountered by the use of this method was that it required two indicating means which had to be correlated in some manner in order that a single indication would be given as to the acceptability of the tested element.

Accordingly, one object of this invention is to provide a completely automatic double bridge for tolerance testing circuit elements wherein only one of a connected pair of high and low limit bridges passes a current at any one time through a single indicating means connected to both of the bridges to give an indication of the magnitude of the element under test.

With this and other objects in view, the invention comprises a pair of Wheatstone bridges having two arms connected in common, one of ,which contains the element to be tested. A single indicating means is connected from a point common to both bridges through a pair of rectifiers as an impedance bridge for testing capacitors and inductors.

Referring now to Fig. 1, a battery II is connected across a pair of Wheatstone bridges I2 and I3 by means of conductors I4, I5 and a switch I6. This battery supplies the bridge circuits with the necessary current for conducting a test. The first bridge I2 comprises four resistance arms which are serially connected in groups of two across the battery II to provide a pair of parallel current branches I1 and I8. The first branch Il' contains a fixed resistor and a fixed standard low tolerance limit resister 2|. The second current branch I8 contains a fixed resistor 22 which is the same size as the resistor 20 and a resistor 23 which is to be tested.

The second Wheatstone bridge I3 comprises four resistance arms which are serially connected in groups of two across the battery II to provide a pair of parallel current branches I8 and 24. The current branch I8 is the same branch as that described in conjunction with the Wheatstone bridge I2. The current branch 24 contains a fixed resistor 25 which is equal in size to the resistors 20 and 22, and a fixed standard high tolerance limit resistor 26.

A pair of rectifiers 21 and 28 of any suitable type, such as a metallic or vacuum tube type rectifier, are serially connected between a midpoint junction 33 of the resistors 20 and 2| and a midpoint'junction 3| of the resistors 25 and 26 through a conductor 32. A current responsive member 33 is connected between the conductor 32 and a midpoint junction 34 of the resistors 22 and 23. The rectifying means 21 and 28'electrically separate the bridges I2 and I3 inasmuch as current'from only one of the bridges is allowed to flow through the meter 33 at any one time.

In the case where the resistor '23 is lower in value than the low limit value of the tolerance range represented by the resistor 2|, the resistors 2B and 22 being equal, the resistor 23 will develop a voltage which is smaller invalue than the voltage developed across the limit resistor 2|. In this manner, the potential at the junction point 30 becomes higher in value than the potential at the junction point 34, thus a current will flow through the rectifier 21 and the directly connected meter 33 to give a visible indication that the resistor 23 is :below the 're quired tolerance range. Inasmuch as the-high limit resistor 23 is larger in magnitude than .the low limit resistor 2I, the potential at the, junction point 3| is higher than the potential at the junction point 34, thus the rectifier 28 cannot conduct and the current flowing through the meter 33 is solely the current flowing from the bridge l2. Since the deflection on the meter 33 is proportional to the flow of current therethrough, the amount by which the resistor is below the/tolerance limit will also be'indicated Wheriithe resistorjabeing tested is larger than the value of the high limit of the tolerance range represented by the resistor 26, the resistors ;22 and 25 being equal, the voltage developedacross the resistor 23 will be higher in value th'anthe 4 limit elements with similar inductors and reversing the polarity of a pair of rectifiers 6| and 62. In the circuit shown in Fig. 3, a transformer 44 is provided for applying an alternating current to a rectifier 45 causing a pulsating direct current to be conducted through a pair of conductors 45 and 41 to a pair of impedance bridges 50 and The firstdmpedance bridge 50- comprises a pair of parallelcurrent branches 52 and 53 which are connected across the power supply leads 46 and 41. The branch 52 consists of a serially convoltage developed across the resiston 25. this v manner the junction point34willwbeat azhigherv potential than the junction pbint '3l}-Jtherefore,

a current will flow throughlthe rectifier, 2&ancl

the directly connected meter'33 to give'an indication that the value of the resistor 23ezis-larger curr -fl wing through the meter. 33 will be "entirely-provided by ;the bridge I3. Since the direcl ioniof .flow. ofo current through the meter V33i1isopnositeito -thatqof; the current flow when thBr:lfBSiStOl23481500, small, themeter 33 will deflect; in a directiongmpposite tothe deflection :whengthe: resistor 23-is. too small thus providing :azmealls :for distinguishing between :the high limit and rlowizlimit; rejections.

I i :Whemthe; size IQf the, {651515013523 is within the ;tolerance mange, the; resistor 23 will :bev larger than the resistor 2| and smaller than the resistor :25; so that ztheyvoltagel developed across the resisim; 23; will. begcornespondingly larger; than that developed across. thecresistor 2 l vandsmaller than ,Zthat whichlsistdeveloped a.cross: the resistor' 2 5. :In'nthis', manner, :the; otential at the -junction point. 34 Will;be largergthan .the potential at the junction point-7 30 landzsmaller than. .the potential ;at2.- the -,jUDCtiOI1'lDOlI1t "H -with. the. result that neither; of "the rectifiersiflz and '28 will conduct. Accordingly?therezwill :.not:;be .angindication on ethes'metert33 ,andT'the-resiston :23 being. tested will "notbevr'ejected. l

modified systemxshowrnin "Fig.1; 2 includes mbiasing: resiston 543 which is. connected between the conducto1z32 and :the junction point: 34,;now

" grounded, in ,:place.1'of the. .current responsive -meter 33. '1 The currentsmroduced imthemanner described hereinb'eforecwhich now'ifiowl through "the resiston 4illproduce' a varyingevoltagel which :is supplied to a direct current! amplifier 4! thro'ughfa coriductor 42. "This voltage is amplified 'by' the amplifier 4| for usein controlling van automatic sorting machine-whichseparates the= elsistor s-into tolerance: groupsaccording to thee oltagereceivedfroin'the resistor 40. In thismannerf'the machine 43 separates the resistors 'into' three groups, namely; an acceptable xgroup' of resistors falling within the tolerance *rangefa rejectedgroup of resistorsfalling below thetolerance'range, and a second rejected group .in whi'ch the-resistors are larger in size than the high' limit of' the tolerancerange.

'Fig'; 3 :shows another modified form of the inventionwhi'ch is adaptedto test the tolerance Y charabteristics-o-of-Eiinpedance "element's. Y Although dztheel circuit shown :isfadaptedx to test :-:ca pacitors, athewirc'uit: cans-,be'rmodifiedsfor; testing inductors bysriepla'icing .ithertest element land'ithei standard 69. --The; current branch; 53 which -is -.-con ne .snected fixed resistance arm 54 and a standard low tolerance limit capacitor 55. :-branch;53:consistseof a serially connected fixed -the resistor 54, an'd a capacitor 51 tobe tested.

The current resistancearm flpwhich is equal to the value of 'I'hersecond impedance bridge 5| comprises two parallel current branches 53 and 58 which are alsoxconnected across the conductors 46 and 41. The current branch 58 consists of a serially con- JJBCtQd fixed resistance; arm 59, which is. equal in yalueito each ofl the resistors 5 4;and 5 a fixed standard: tolerance. hig h limitcapa tor in common with bothof the'bridges; 50- an is described in conjunction with therdesgl" of bridge 50. @The rectifier-s61 andBZ are erially connected betweenna, midpoint,;63 of. .theebranch 52 and a midpoint-fi lofvthe; branchg 58 throu h a conductor, 65.,-;A fixedgresistor; fifi connects th conductor 55 to a midpoint filiofpthe branc 53.

The "operation of the;bridges 50 1 and 1 5 1- {is the same as that ,describedin; conjunctiomwithl li i s. 1 and 2 with theeXQeption; that the YCCbiflBlififfi I and! areireversedxin polaritypvfrompthe rectivoltage across inductors varies 1directlya'witl xthe size of the inductiveaelementl The yarying voltage developed acrossithea-resis- :tor;v 66 in accordance withjthecprinciple:.ofwthe :invention: may be applied :ato; a directs-current amplifiecta through a conductor 69. .:'Ihe:--amplified voltage frorn the-amplifier "68' maybe used to energize any suitablemtype of automatic sort- 'ing ma'chine l0 whereby the tested-elements may be separated intoknown tolerance: groups Inoperation; before any -tests are made; the proper high and lowlimitelements are -selected and connecteddn the circuit. Following this an element tobe tested'isconnected"intothe-porrect position in the com mon arm of "theftwo bridges. With the; elementto be tested in' the circuit, it is only. necessary to read the, meter for an indication oofnthe sizeof the elementunder test. time element may ,then' be manually placed in thepropertolerancev grouplonas inthe mod-i- .fied ,the element {Will -be automatically shunted-into the proper-tolerance;group by the .inachine 43' or: 13. fThe1&fOI',8,- itis only neceslier the test. :GD I'aIEOE'KtO place: (the: element in; momentary :GOIltfiCt tWithi? the. bridges. arm #in order: to. gain an automatic:indication of' the size @of: the: elementea-Thusain this manner xitiispossible to test a large number of elements in a very short period of time.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A system for automatically testing a circuit element for certain requisite tolerance characteristics comprising a source of current, a first Wheatstone bridge energized by said current source, said first bridge having a first detecting current junction, a second Wheatstone bridge energized by said current source simultaneously with said first bridge and having two arms connected in common with the first Wheatstone bridge, one of said common arms containing the element to be tested, said second bridge having a second detecting current junction, an indicat ing means connected to the junction of the common arms through a first terminal, and rectifying means selectively connecting a second termi nal of the indicating means to the first and second detecting current junctions for providing the indicating means with a current from one of the bridges to produce an indication of a characteristic of the element under test.

2. A system for automatically testing circuit elements for certain requisite tolerance charac teristics comprising a source of current, a pair of Wheatstone bridges having two common arms, one of the common arms containing an element to be tested, each of said bridges having a detecting current junction, a pair of rectifying means connected to and selectively separating the two detecting current junctions, and a common indicating means connected from a point between the pair of rectifying means to the junction of the common arms for providing an indication of a characteristic of the element under test.

3. A system for automatically testing circuit elements for certain requisite tolerance characteristics comprising a source of current, a first Wheatstone bridge energized by said source and including an element to be tested and a standard low limit branch, said low limit branch having a detecting current junction, a second Wheatstone bridge energized by said source simultaneously with said first bridge and including a standard high limit branch and having another branch including the element to be tested connected in common with the first Wheatstone bridge, said high limit branch having a detecting current junction, and an indicating means including a plurality of rectifiers serially connected between the detecting current junctions and the element to be tested whereby a single unidirectional current is applied to the indicating means for determining the classification of the element in the tolerance range.

4. A system for testing circuit elements for certain requisite tolerance characteristics comprising a source of current, a first resistor and a low limit resistor connected across said current source, a second resistor equal in value to the first resistor and a resistor to be tested serially connected across said current source, a third resistor equal in value to the first resistor and a high limit resistor serially connected across said current source, a pair of rectifiers serially connected between the high limit resistor and the low limit resistor, and an indicating means connected from a point between the two rectifiers to the junction of the second resistor and the resistor to be tested for detecting voltage unbalance across either of the high or low limit resistors.

5. In a system for tolerance testing circuit elements in succession and sorting them into low, high and satisfactory classifications, a source of current, a low limit bridge connected in parallel with the current source, a high limit bridge connected in parallel with the current source, said bridges having two arms connected in common, one of the common arms containing the circuit element to be tested, an indicating means connected through its first terminal to the junction of the said common arms, and rectifying means selectively connecting a second terminal of the indicating means to other junction points of the low and high limit bridges to permit fiovv of current through the indicating means from only one of the bridges at any one time.

6. In a system for successively testing and sorting resistor elements into low, high and satisfactory classification groups, a source of current, a first resistor and a low limit resistor connected across said current source, a second resistor equal in value to the first resistor and a resistor to be tested serially connected across said current source, a third resistor equal in value to the first resistor and a high limit resistor serially connected across said current source, a pair of rectifiers connected in series between the low limit resistor and the high limit resistor, a fourth resistor connected at a point between the two rectifiers to the junction of the second resistor and the resistor to be tested, an amplifier connected to the fourth resistor, and a sorting device connected to and controlled by the amplifier for separating the tested resistor elements into the said three classification groups.

7. In a system for successively testing and sorting impedance elements into low, high, and satisfactory classification groups, a source of current, a first resistor and a low-limit impedance connected across said current source, a second resistor equal in value to the first resistor and an impedance to be tested serially connected across said current source, a third resistor equal in value to the first resistor and a high-limit impedance serially connected across said current source, a pair of rectifiers connected in series between the low-limit impedance and the highlimit impedance, a fourth resistor connected at a point between the two rectifiers to the junction of the second resistor and the impedance to be tested, an amplifier connected to the fourth resistor, and a sorting device connected to and controlled by the amplifier for separating the tested impedance elements into the said three classification groups.

JOSEPH C. BREGAR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,985,095 Hoare Dec. 18, 1934 2,033,465 Graham Mar. 10, 1936 2,283,072 Leathers May 12, 1942 2,456,499 Fritzinger Dec. 14, 1948 2,468,625 Goetz Apr. 26, 1949 2,505,072 Sunstein Apr. 25, 1950 

